Скачать или смотреть Understanding the Mistake in Your JavaScript 'if' Statement for Domain Validation

Learn why your JavaScript 'if' statement for validating user domains is not working and discover how to fix it effectively.
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This video is based on the question https://stackoverflow.com/q/63105572/ asked by the user 'John Deacon' ( https://stackoverflow.com/u/10959190/ ) and on the answer https://stackoverflow.com/a/63106253/ provided by the user 'Adrian Brand' ( https://stackoverflow.com/u/1679126/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Mistake in Your JavaScript 'if' Statement for Domain Validation

When writing JavaScript code, especially when dealing with asynchronous operations, it is easy to run into issues that can cause your code to behave unexpectedly. One common problem arises from not fully understanding how promises work, particularly when using them with conditional statements like if. In this guide, we'll explore a specific issue related to a domain validation check in your code and how to resolve it effectively.

The Problem: An Unresponsive 'if' Statement

The code block in question is intended to check if a user's current domain (extracted from the URL) matches any domain listed in a predefined array. This check is performed using the following if statement:

[[See Video to Reveal this Text or Code Snippet]]

Despite this condition appearing to be in place, the problem is that the recommendations API is executing regardless of the domain the user is on. Let's dive into the root cause of this issue.

Understanding Asynchronous Execution

The core of the problem lies in how the JavaScript function browser.storage.local.get works. Here are a few key points to consider:

Asynchronous Execution: The function returns a promise that is executed asynchronously. This means that while the promise is waiting to resolve, the rest of the block of code continues executing without waiting for that condition to be satisfied.

Placement of Return Statement: The return statement inside the if does not stop the execution of subsequent code that comes after the promise. As a result, the function containing the API call is executed regardless of the domain check.

The Solution: Refactoring the Code

To resolve this problem effectively, you'll need to refactor your code to ensure the checks are done correctly before proceeding to call the API. Here’s how you can do that:

Step-by-Step Refactoring

Encapsulate the API Call in a Function: Start by creating a separate function that handles the API call. This will isolate it from the domain check logic.

Adjust the Conditional Logic: Modify the conditional statement to use this new function only if the domain matches.

Here’s an example of how this can be implemented:

[[See Video to Reveal this Text or Code Snippet]]

Explanation of the Modifications

New Function: The callUrlFunction now houses the API call logic, ensuring that it only executes when the domain check is successful.

Logical Flow: The if condition now directly controls when the function gets called, preventing unnecessary API calls when the user's domain does not match.

Conclusion

By understanding the nuances of JavaScript's asynchronous behavior and restructuring your code accordingly, you can make your domain-checking logic effective. Ensuring that your if statement correctly controls the flow of execution is crucial in preventing errors such as premature API calls. With these changes, you will have a more robust function that behaves as expected.

Using clear separation of logic and respect for asynchronous execution can significantly improve your JavaScript coding practices. Happy coding!